One mechanism for infection of a host cell by a microbe, such as a virus, a bacterium or a protozoan, proceeds via initial attachment of the microbe to the host cell surface. This process is mediated by relatively weak attractive interactions between adhesion molecules on the surfaces of the microbe and the host cell. In general, microbe-host cell attachment is the product of a multiplicity of such interactions, via what has been referred to as the polyvalent effect. One well-studied example of such a process is the attachment of the influenza A virus to mammalian epithelial cells, which results from interaction of terminal N-acetylneuraminic acid groups of glycolipids and glycoproteins on the host cell surface with the attachment glycoprotein hemagglutinin on the viral surface.
The scarcity of effective antiviral agents points to the need for new approaches to the treatment of viral infections. The attachment step is an attractive target for such a treatment, and much activity has focused on the development of N-acetylneuraminic acid-containing compounds capable of binding to viral hemagglutinin, thus inhibiting viral attachment to host cells. Studies have demonstrated that polyvalent compounds, such as polymers bearing pendant N-acetylneuraminic acid groups, bind influenza virus with association constants which are several orders of magnitude higher than those of monomeric N-acetylneuraminic acid derivatives. To date, no polyvalent N-acetylneuraminic acid containing compounds are in clinical use for treatment or prevention of influenza. Moreover, no data demonstrating in vivo efficacy of such compounds have yet been published.
A disadvantage of N-acetylneuraminic acid-functionalized compounds as therapeutic agents for the treatment of infection by influenza A virus and, possibly, other viruses, is the great expense of this sugar. In addition, the influenza virus has at its surface the enzyme neuramidinase, which cleaves N-acetylneuraminic acid moieties from such molecules, eventually destroying their ability to bind the virus. There is, thus, a need for inhibitors of viral attachment to mammalian cells which have an improved efficacy, are readily prepared from inexpensive starting materials and have a broad spectrum of activity.